Hydraulic power aligning mechanism



Feb. 24; 1953 R. A. POLSON 2, 2

HYDRAULIC POWER ALIGNING MECHANISM Filed Sept. 26, 1946 :1 4*" 'l H lol 2 E 5 1 49 I INVENnm.

ATT NEYS Patented Feb. 24, 1953 W HYDRAULIC POWER ALIGNING MECHANISM Reginald Alexander Polson, Manchester, England, assignor to Metropolitan Vickers Electrical Company Limited, London, England, a company of Great Britain, and Vickers-Armstrongs Limited, London, England, a company of Great Britain Application September 26, 1946, Serial No. 699,432

, In Great Britain April 28, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires April 28, 1963 13 Claims. (01. 60-53) This invention relates tocontrol systems for maintaining power driven movable objects in alignment or other desired positional relationship with a directing means. In control sys tems of this kind means responsive to the misalignment of the movable object with respect to the directing member are arran ed t l l the motive equipment which drives the movable object so thatthere will be applied to the movable object a torque or force which reduces to zero the misalignment between the movable object and the, directing member. In particular, the invention provides a system of the kind set forth which controls the supply of operating fluid to a hydraulic motor which drives the movable object. H

Alignment control systems which respond onlynto the misalignment between the directing means and the movable objectare generally unstable and tendto produce an oscillation of the movableobject about the position corresponding to exactalignment; with the directing member. In some cases this oscillation is self-sustained. Such oscillation of the movable object, whether self sustainecl or only lightly damped, isespecially likely to occur where the control system isrequired to cause rapid movements of the movable object to reduce misalignments between it and the,directin member. u

The principal feature of this invention is the provision of a control, system of th kind set forth above which effects rapid and exact reduction of misalignment between a power driven movable object and its directing member, and which is stabilized to prevent undesirable-oscil lations of the movable object about that location which corresponds with zero misalignment between the movable object audits directing memberg To achieve this feature of my invention, I have arranged my control system to be depends 1 tion, or third time derivative of the misalignent in its operation not only upon the relative displacement between the movable object and the position it must assume to bein alignment with the directing member, but also u'pon'one or :mere orders of the rate of change of the displacement of the movable object with respect to the position it must assume to be in alignment with the directing member, 1. e. the rate of change, or first time derivative, of the misalignment which may be termed the velocity of the directing member with respect to the movable ment which will be referred to as such. To efiect this, the control system is caused to introduce in opposition to the force or torque applied to the movable object a control quantity which is representative of one or more orders of the rate of change of misalignment. This results in two desirable effects. As the movable object "approaches the position of zero misalignment, the components of the torque representative of the velocity, acceleration, and rate ofchange of acceleration opposes the motion of the object and 'damps any tendencyit may have to oscillate about the position of zero misalignment. When the movable object is required to follow' rapid movements of the directing member the component of the torque proportional to the relative velocity of themovable object with respect to its position of zero misalignment with the directing member facilitates response to rapidchanges in direction and velocity of thedirecting member.

According to my invention, means responsive to the misalignment of the movable object with respect to its directing member, which means may or may not also be responsive to the rate of change of that misalignment, controls the sup,- ply of operating fluid to a hydraulically operated power source for the movable object. Addi? tional means responsive tothe' change-in pres.- sure of the operating fluid and to therate of change of that pressure are provided which suppressively feedback into a summating means control quantities representative of this change and rate of change of pressure. Since the change in pressure across the hydraulic power source is proportional to the torque or force applied to the movableobject and the torque or force applied to the movableobject is representative of the acceleration of the movable object with respect to the directing member, the, change of pressure and rate of changeof'pressure are representative respectively of-the second and third time derivatives of the misalignment of the movable object with respect to the directing member.

These control quantitiesare introduced into thesummating means through means selectively responsive to values of the control quantities greater and less than predetermined values. In the event thatthe value of thecontrol quantities exceeds the predetermined value the selectively responsive means transmits only the component representative of thesecond time derivative or acceleration. When the value of the control quantities is less than the predetermined value, the selectivelyresponsive means transmits to the summating means proportional amounts of the second and third time derivatives of the misalignment and the summating means imposes these quantities on the action of th means responsive to the misalignment and velocity of misalignment. Stabilization of the response of the movable object to the directing member is thereby obtained.

A complete and detailed description of two embodiments of my invention is contained in the following specification. This description will be readily understood by reference to the attached drawing in which Fig. 1 is a schematic representation of one hydraulic control system embodying my invention; and

Fig. 2 is a schematic representation'of another hydraulic control system embodying my inven tion.

Referring now to Fig. '1 .a movable object to be directed, such as an artillery'piece3 on a rotatable 'mount, and a directing member, such as an aiming telescope '4 on a rotatable mount, are interconnected "to means responsive to misalignment of the movable object with respect to the directing member. These means may be of any suitable kindbut in this description will be assumed to comprise an electrical system of the Selsyn type which determines the energisation of a moving coil relay. This moving coil relay is similar to that shown in and described with reference to Fig. '2 of United States Patent No. 2,533,042,'issued December 5,1950.

The rotatable mount for the artillery piece '3 is driven through shaft 1 by a reversible hydraulic motor 6 which is supplied with operating fluid under pressure through ports 8 or I!) depending on the desired direction of rotation. These ports are connected by conduits H and i2 witha variable delivery pump 13 adapted to circulate operating fluid through the hydraulic motor in one direction or the other between the ports .8 and T0. The rate of circulation of the operating .fluid is determined by a control member so that the speed and direction at which the hydraulic motor is operated will be proportional to the displacement of the control .member H in one directionor the other from its'illustra tedneutral position.

The hydraulic motor '6 andpump "IBmay, 'for example, comprise ahydraulic transmission providing an infinitely variable velocity ratio .be-

tween the means driving the pump 13 and the motor "6 of the type known as a variable speed transmissionin which'the delivery of the pump 13 is controlled by the inclination of a swashplate, the inclination of this swashplate being proportional to the displacement of the control member 14.

The control member TI 4 is actuated by a double acting fluid pressure servo mechanism, being coupled with a piston l5 of said mechanism. Thispistonis movable within a cylinder l6 have iing its two ends connected with control ports 'I"! and I8 of a control valve 2 which is.provided with aninlet port 21 which, by way .of a conduit partially shown at 22, is connected with a source of operating fluid under pressure. In the illustratedzposition of-the movable member 23 of the control valve 20, flow of fluid to the cylinder 16 is obstructed, but fluid will be supplied to the right or'left-handside of'the piston I by movement of the member 23 to the right or left ofthis closed position. Of course, the valvemust allow discharge of flu'id from the other side of the pis- '4 ton for return to the source. The rate of movement of the piston l5,.and thereby of the control member [4, will therefore be dependent in direction and speed upon the sense and extent of displacement of the valve member 23 from the closed position.

The member 23 of the control valve 20 is connected (in a manner more particularly described hereinafter) with the moving coil relay device 5 so as to receive a displacement which is dependent upon the misalignment between the artillery piece and the telescope. A convenient electrical circuit for this purpose is illustrated in Fig. l "of the above mentioned Letters Patent. The displacement of the moving coil relay device will include not only a component dependent on the misalignment, but also a component dependent upon the first time derivative of said misalignment, that is to say upon the relative velocity between the artillery piece and the directing telescope. The displacement of the valve member 23 of the auxiliary control valve is further modified as hereinbefore set forthby a particular means hereinafter to bedescribed, but it may be stated now that, with the control system asso far described, the control valve?!) will operate to cause movement of the piston l5 in one direction or the other at a speed and in a direction dependent on the extent and sense of misalignment between the movable object and control member, and more particularly dependent on the magnitude and sense of acontrol quantity comprising the sum of component dependent respectively upon the misalignment-and the rate of change of said misalignment. The movement of the servo piston I5 in this manner will cause, by the setting imposed on the control member [4, a corresponding change in the velocity of the artillery piece until the displacement of said member [4 from the central position thereof becomes just sufficient in one orthe,

other direction to cause movement of the artillery piece with a velocity corresponding 'to the velocity of the directing telescope and with substantially zero misalignment. As this condition of alignment is effected, the relay device tends to return the auxiliary control va1ve23 to'its illustrated central position.

The stabilising means according'to the invention asembodied in the control system o'fiFig. 1 comprises a pair of pistons '24 and 25 working within their'separate cylinders 26and 21 which are connected by means of conduit 2'8 and 30 respectively with the ports 8 and 10 of the hydraulic'motorfi. The pistons 24 'and 25 arepiv otally connected with an intermediate point tl of a lever 32 having a fixed pivot at33. The-two pistons act in opposition to one another'on said lever whereby the resultant force applied-by the pistons to the lever 32 is dependent upon the pressure difference existing between the ports '8 and I!) of the motor'and'is, therefore, representative of the torque applied to the'mounto'f the artillery piece. The lever 32 is provided with compliant means such as springs 34 biasing th'e lever to the illustrated central position. The free end of the lever is connectedby-means ofa link 35'and a dash pct 36 with one end o'f-a floating lever 31, which is biased'by compliant means such asspring 38 to the illustrated central position thereof. The other end of the floating lever 31 is connected by a link with themoving-coil relay device 5. An intermediate point-"4| of the lever 31 'is connected by means of a link 42 with the valve member 23-of the control valve. This at the port artillery piece.

floating lever constitutes a summating mechanism. The total effect produced by this arrangez'n'ent is such that a change in the pressure across the hydraulic motor will tend to reset the conthe control valve 23 to allow fluid to flow from the conduit 22 through the port H to the right hand side of the piston [5, thereby moving the control member 14 to the left.

This movement causes fluid to circulate through the motor from the port 8to the port H). The

pressure at the port 8 being greater than that ID, the piston 24 displaces the lever 32 against the springs 34 in the clockwise direction and by an amount proportional to'the differential in pressure between the ports, and consequently, to the torque applied to the The rate of change of the pressure differential at the ports will also be reflected in the motion of the lever 32. Since the torque applied to the artillery piece determines its acceleration, the pressure diiierential at the ports which determines the torque is related to the acceleration of the artillery piece with respect to the directing telescope, it being the second time derivative of the misalignment. It follows that the rate of change of the pressure differential is related to the rate of change of acceleration of the artillery piece with respect to the directing telescope which is the third time derivative of the misalignment. Thus, both the second and third time derivatives of the misalignment appear as components of the motion of the lever 32.

The motion of the lever 32 is transmittted through the dash pot 36 to efl'ect a leftward displacement of the upper end of the floating lever 31. The dash pot 36is adjusted so as to transmit movement of the lever 32 to the lever 31 for changes and rates of changes of the pressure differences corresponding with the accelerations involved in the required speed and direction of response of the artillery piece to changes in speed and direction of the directing telescope. For such changes and rates of changes of pressure, the dash pot will transmit to the upper end of the lever 31 a force which is dependent upon the displacement of the lever 32 and which is also dependent in part upon the rate of change of said displacement. Consequently there will be superimposed on the opening of the control valve 20 by the moving coil relay device 5 a movement which is dependent upon the second and third time derivatives of the displacement of the artillery piece with respect to the directing tele scope. For rates of change of pressure in excess of predetermined values dependent on the characteristics of the dash pot and the bias spring .38, the dash pot transmits movement solidly forth.

It will be understood that in place of the dash pot 36 any other suitable means adapted to transmit a force varying with the velocity of movement between two co-operating partsgof said device, which parts are coupled respectively with the lever 32 and with the upper end of the lever 31, may be employed.

In a modified arrangement of the control system according to the invention shown in Fig. 2, there is illustrated an alternative form of control of the hydraulic motor. The motor is supplied with operating fluid through conduit 51: by a suitable constant pressure variable delivery pump. The flow of fluid is controlled by athrottle valve 56 which may be of the piston type shown. The control ports 53 and 54 of the throttle valve are connected respectively to ports 8 and ll] of the hydraulic motor 6 by conduits II and I2. While the control member 55 of the valve 56 is in the position illustrated in Fig. 2, the flow offluid to ports 8 and I0 is blocked, whereas the valve will permit fluid to be supplied to port 8 or ID as the control member is displaced to the left or right of the central position shown.

After passing through the motor the fluid returns through port 54 Or 53, as the case may be, and is returned to the reservoir of the pump. The operating fluid is supplied to the motor, at a rate dependent on the extent of the displacement of the control member 55 from the illustrated central position. By this means the artillery piece will be rotated at a speed which is likewise dependent on the extent of the displacement of the control member.

The control system of Fig. 2 has pressureresponsive pistons 24 and 25 whose operation on the lever 32 is related to the pressure difierential across the motor as in the system of Fig. 1. However, instead of the free end oflever 32 being connected directly to an element of the dash pct 36 by the link 35, the link 35 interconnects the free end or" lever 32 and one end 44 of a second floating lever 43. An intermediate point 45 of this second floating lever is connected to one element of the dash pot by link 49 and the opposite end 46 of the lever is connected to the control rod of the piston l5 which actuates the throttle valve 58. This floating lever is asummating lever which transmits to the dash pot the algebraic sum of the first, second and third time derivatives of the misalignment. The dash pot transmits this combined control quantity accordingly as the value of the control quantity is less than or greater than predetermined values related to the response characteristics of the dash pot and spring 41.

The other element of the dash pot is connected to one end 50 of a floating lever 48, constituting another summating mechanism, and is biased'to the position illustrated by the spring 41. In the same manner as in Fig. 1, this lever 48 is connected at an intermediate point 5| to the control member 23 of the valve 20, and at the opposite end 52 to the moving coil relay device 5.

In the operation of the control system shown in Fig. 2 the displacement of the point 45 of the floating lever 43 will be proportional to the algebraic sum of the displacements of the lever 32 and the piston [5. In other words, the upper and lower ends of the floating lever 43 are respectively displaced by amounts related to the pressure differential across the motor and the a movement which is-transmitted to the dash pot es "l 3 6. This movement, due to the -..component of motion-of the intermediate point 435 of "the float- -ing lever 43 dependent .upon the .pressure applied to the hydraulicmotor, :will be dependent uponthe second and third time derivatives of the .displacement :of the artillery piece with respect to thedirec'ting telescope as above described with reference to Fig. 1. Furthermore, due to the *componentof motion of the intermediate point E5 of "leve1- 43 derived from the-connection at at of the floating lever 43 with the piston l5, -a component proportional to the-rate-of supplyo'f liquid to the motor, the motion of lever 33 at point *45 will include a component dependent upon the telocity or first time derivative of the displacement of the artillery piece. It will-also be apparent that "over a certain range of rates of change of said velocity of the artillery piece, lthatisto say rates of change of position of the servo piston t5, the motion of "the point will include a "further variable component dependent upon the second time derivative of the displacement of theartillery piece with respect to the directing telescope. As the output of the floatingleverfiSis transmitted through the dash pot in accordance with criteria imilar to those stated for theembodiment of Fig. 1 there is imposed on .the output of the floating lever 48 a control quantity which opposes the response of the motor to gros indications of misalignment and velocity .of changes-of misalignment between the direct- .ing telescope and'the artillery piece, and bythis ;means stabilisation of the control system is obtained.

In some applications of'thearrangernent shown in Fig. 2 the moving coil device 5 or equivalent rmisalignment responsive means may satisfactorily be arranged to respond only to the misalignment of the artillery piece with respect to "the directing telescope without the inclusionof a. 'component dependent upon a time derivative of said misalignment. This follows from the fact that the extent to which the control valve 29 'or-other means determinative of the velocity of themotor is-actuatedde'termines the velocity of the artillery piece with respect to the directing telescope, and a control component representative of velocity is'fed back intothe system by the: lever 453. Itwill thus be understood that in the arrangement shown in Fig. 2 theelectrical circuit "for the movingcoil-relay device 5 may be modified .so as to omit the component in the-energisation of said device dependent upon the rate of change of the misalignment.

In modifications of the control systems "above described the moving coil devices 5 'may 'be replaced by means according'to United States Letters Patent No. 2,533,042 for couplingthe lower ends of the floating levers '3? and 48 with means responding to the 'misalignment between 'the ar tillery piece and the directing "telescope and "for adding to the motion of 'the'lower end of said levers components dependent upon the rate of change of movement of said misalignment responsive means.

' 'Itwill'be understood'thatthe summating'mechanisms of Fig. 2 may be employed for controlling the variable speed transmission i3 indicated 'in Fig. .1, and that th summating mechanism of Fig. 1 maybe employed:forcontrolling the throttle valve .56 shown .in .Fig. 2. Furthermore, either .of themechanismsmay be-employed for control ling the pressure applied to the hydraulic :motor ating elementiorsai'd first-control means, to the 'splacements of which th velocity of saidmotor is-related;.a second control means operatively con- :nected with=saidzfirst actuating element; a sum- :mating mechanism producing .as outputa motion whichis .a function of the :algebraic sum of two inputs; a second actuating element for saidsecond controlmeans, to the gdisplacementsof which the velocity-of said'first actuating element and, :therefore, theacceleration of .said ;m0tor:are1related, eifectively connectedto the o-ntputof said eliminating rinechanisxn "means eiiectively transmitting "nusalignment between said movable object and said directing .member ;as one input to saidsummating mechanism; means .responsivetc the hydraulic pressure differenial across said Lmotor; a firstcompliant :means limiting the response of. said means ;resp onsive to the hydraulic pressuredifierentialito an amount related to that pressure differential; a dash pot effectively connected .at-one side to said responsive means and at the other side to produce the other .input "to :said:summatingmechanisrn; ,andpa second ,com-

pliant means effectively connected to said other side of said dash pot andlimitingthe displacement thereof to amounts proportional to :the force transmitted by said dash not from "said means responsive to the hydraulic pressure differential, whereby the effective connection of:said

directing member into the system is reset-when ranged to impose on said dash pot a force=proportional to the displacementof the side of the dash pot to which said spring is connected.

3. The combination of claim 2=in which :means areprovided responsive to thedegree of:actuation of the firs't control means operatively-coup'led to the second actuating means through ithe dash pot, whereby there is further superimposed -on :the response of thecontrol means-acomponent dependent on changes in the rateofsupply of :liquid to the motor and thereby upon the rat-e of change of velocity thereof and in a direction tooppose changes insaid velocity.

'4. The combination of claim 3 in which the :dash pot has its cooperating elements coupled respectively with the :second actuating element :and with the output element of :a 'surnma'ting mechanism, the inputclements ofxsaid summating mechanism being coupled respectively with the means responsive to the hydraulic pressure .diiferential across .said .hydraulic .motor and the means responsive to the degree of actuation of .the first-controlmeans.

5. The combination of claim .4 in whichxthe summating mechanism consists of ;a floating lever, the input and .output elements .of :said mechanism being constituted by difierent points .of-saidlever.

6. The ,combination :of claim 15 in {which 113118 first control means is actuated :by a 2flu'id .zservo device, a control valve of which is coupled with or forms the second actuating element.

7. The combination of claim 1 in which the efiective connection between the dash pot and the directing member includes coupling spring means arranged to impose on said dash pot a force proportional to the displacement of the side of said dash pot to which said spring means is connected and is transmitted through a summating mechanism, one input element of which is coupled to the side of said dash pot connected to said directing member, one input element of which is coupled to said directing member, and an output element of which is coupled to the second actuating element.

8. The combination of claim 7 in which the summating mechanism is a floating lever, the input and output elements of said mechanism being constituted by difierent points of said lever,

9. The combination of claim '1 in which the motor is supplied with operating liquid from a constant pressure variable delivery source and the first control means is a reversing valve intermediate said motor and said source.

10. The combination of claim 1 in which the hydraulic motor is the output part of a variable speed transmission of the multiple swash plate type.

11. The combination of claim 10 in which the first control means is a variable inclinable swash plate in the pump part of the variable speed transmission.

12. In a hydraulic power aligning mechanism including a movable directing member, a movable object to be aligned with said directing member, a hydraulic motor driving said movable object, a first control means directly controlling the supply of operating liquid to said motor, and a second control means for actuating said first control means in accordance with the misalignment of said movable object with respect to said directing member so that said motor produces a torque tending to reduce said misalignment to zero, the improvement which includes in combination a first summating means, means responsive to the fluid pressure applied to said motor coupled to one input element of said first summating means, means responsive to the degree of actuation of said first control means coupled to another input element of said first summating means, a dash pot, a second summating means, an output element of said first summating means coupled to an input element of said second summating means through said dash pot, means responsive to the misalignment between the directing member and the movable object coupled to another input element of said second summating means, and a second actuating element of said second control means controlling the actuation of said first control means coupled with an output element of said second summating means.

13. The combination of claim 12 in which the summating means are floating levers, the input and output elements oi said summating means being constituted by different points of said levers.

REGINALD ALEXANDER POLE-ON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,372,502 Grun Mar. 22, 1921 2,056,896 Douglas Oct. 6, 1936 2,077,384 Dettenborn Apr. 20, 1937 2,104,627 von Manteufiel Jan. 4, 1938 2,188,834 Fischel et al. Jan. 30, 1940 2,238,061 Kendrick Apr. 15, 1941 2,285,069 Vickers June 2, 1942 2,291,011 Vickers July 23,1942 2,408,070 Hull Sept. 24, 1945 2,409,190 Brown Oct. 15, 1946 2,533,042 Poison Dec. 5, 1950 FOREIGN PATENTS Number Country Date 453,928 Great Britain June 17, 1935 

